1. Field of the Invention
The present invention relates generally to construction techniques and to line transfer instruments and their use in particular.
2. Discussion of Background
Accuracy in construction of buildings, walls, highways and drains is an important goal. However, two factors tend to operate to reduce accuracy in construction: the construction environment and time. Construction by and large takes place out of doors, in the elements, and on terrain that may not make it easy to be accurate with measurements. Furthermore, construction jobs are often competitively bid and required to meet a schedule; therefore, time cannot be wasted, or if the job falls behind schedule, time must be made up.
An important part of construction is setting a line, that is, establishing a direction in three dimensional space to guide construction. The line may be used to determine the direction in which a pipeline is to be laid, for example, or the location where certain structures will be built. The line transfer instrument is a common piece of equipment used in construction to set a line. A typical line transfer instrument is a sighting device, or simply a xe2x80x9cscopexe2x80x9d, mounted on a tripod or base. In laying pipe, for example, it will be used in cooperation with a pipe laser. The purpose of the pipe laser is to establish a beam of light down the center of the pipe as each section is added to it. Each section of pipe is centered on the beam using a target temporarily placed over the end of the pipe. If the laser beam shines on the center of the target, that pipe section is aligned with the preceding sections. However, the line transfer instrument is used to set the direction of the pipe laser so that it is pointing in the correct direction.
To set the pipe laser in the case of a sewage or drainage pipe, a manhole is put into position and the pipe laser is lowered into it. Perhaps one or two sections of pipe are connected to the manhole that run in the general direction the pipe line is to go. The line transfer instrument with its tripod is placed on top of the manhole and centered by eye over the pipe laser and leveled. The centering of the line transfer instrument over the pipe laser is then refined using a plumb bob. Usually an assistant is sent into the manhole to limit the swinging of the bob. If the line transfer instrument is not centered, screws holding it to the tripod are loosened so it can be moved laterally and retightened. When centered, the line transfer instrument is directed at the distant marker, which indicates where the pipe line should be directed. Then the scope of the instrument is angled downward until it is looking at the laser light emitted by the pipe laser. If the pipe laser is not pointing its beam of light in the correct direction, it is redirected. In the case of many pipe lasers, redirection can be done using a remote control device.
This process is not as simple as it sounds. The tripod is perched somewhat precariously on top of the manhole where the opening is not centered over the center of the floor of the manhole, where the pipe laser is located. Sometimes the center of the pipe laser cannot be seen or is difficult to see at the bottom of a dark manhole. The plumb bob, especially if it hangs from a long wire, will swing interminably and at the least disturbance. Shifting the transit requires releveling the transit and waiting for the plumb bob to stop. Meanwhile the weather may be cold, windy and rainy.
There remains a need for a line transfer instrument that is easier and quicker to use.
According to its major aspects and briefly recited, the present invention is a builder""s level transit having a self-leveling sighting device or scope capable of being rotated over a wide arc, including several degrees of arc past vertically downward, and a base for the sighting device carrying means for controlled translational movement of the sighting device horizontally, perpendicular to the optical axis of the scope. Preferably, the scope also carries a laser spotter that can be used to illuminate the surface of the pipe laser in the manhole to help with focusing on the scope when centering the line transfer instrument. A small, relatively wide angle spotting telescope is mounted to the top of the scope of the line transfer instrument to make it easier to set up the device initially. In addition and optionally, the scope is held in place by a radial arm clampable to a manhole rather than a tripod.
To shoot a line, the radial arm is clamped to the manhole and leveled. Using the spotting telescope, the user sights on the distant marker and then uses it and the laser spotter to look down at the pipe laser. If the line transfer instrument is within a few inches of being centered on the pipe laser, the user will redirect the scope at the distant marker and sight it between the cross hairs of the scope and lock that azimuthal position in with a position lock on the base so that the scope cannot rotate about a horizontal plane.
The user will then rotate the scope back down at the pipe laser, about a vertical plane, and translate the scope laterally until the center of the pipe laser is in the cross hairs of the scope. Next, the user will sight on the pipe laser""s laser light where it emerges from the end of the pipe laser and, using the remote pipe laser rotating control, turn the pipe laser until its laser light beam is aligned with the cross hairs of the scope. The pipe laser is then pointing in the right direction. As long as the laser light from the pipe laser hits a target centered in the sections of pipe added, the run of pipe will be following the line established to the distant point.
The ability to translate the scope laterally without moving the base is a major advantage of the present invention. Because it can be moved laterally without loosening it from its base and releveling it and resighting on the distant point, the user is able to align the pipe laser with the distant target much faster.
Another important feature of the present invention is the combination of the scope that can be directed a few degrees past straight down and the laser pointer it carries. This combination allows the user to see the center of the pipe laser in the manhole from the scope more quickly because the laser spotter illuminates the pipe laser""s otherwise dark surface.
Another feature of the present invention is that the scope optics allow focusing at a much closer range than conventional line transfer instrument scopes. In finding the center of the pipe laser in the manhole, having the magnification of the scope and the ability of the scope to focus on the surface of the laser allows the cross hairs of the scope to be more quickly and accurately brought in line with the center of the laser than by using a plumb bob.
Other features and their advantages will be apparent to those skilled in the art of level transits from a careful reading of the Detailed Description of Preferred Embodiments accompanied by the following drawings.